Scientists say they have successfully extracted DNA from an anatomically modern man who died on the shores of an Australian lake about 60,000 years ago. The sequence is so primitive that it raises questions about the leading model of human origins, the "Out of Africa" theory, which holds that our ancestors first arose in Africa, then spread throughout the world perhaps 100,000 years ago.
DNA studies from living populations have repeatedly pointed to a recent African origin for humans. By analyzing variations in modern DNA sequences and tracing their "roots" backwards in time, scientists have concluded that everybody now alive stems from African ancestors who replaced earlier types of humans without interbreeding. But another model, called multiregionalism, is favored by a determined minority of anthropologists. They suggest that people coming from Africa interbred with earlier humans already living in various parts of the Old World.
The underdog theory may gain some support. A team led by anthropologist Alan Thorne of Australia National University in Canberra says that they extracted mitochondrial DNA (mtDNA) from 10 fossils, including a 60,000 year-old-man known as LM3 who was found near Lake Mungo. LM3 is "possibly the oldest human from which DNA has been recovered," Thorne says. Even more intriguing, the scientists identified a sequence that is now extinct in human mtDNA, they report in an online manuscript that will appear in the Proceedings of the National Academy of Sciences. Thorne says the fact that an Australian--and not an African--has yielded the most primitive-looking DNA yet found in an anatomically modern human is strong evidence that not all our ancestors stem from Africa.
"For many years people have been saying Out of Africa is correct because the genetic evidence is consistent," says John Relethford of State University of New York College at Oneonta. But the Australian study "suggests that if we saw more ancient sequences we might get a very different picture than we get from looking only at the DNA of living populations."